1. Field of the Invention
An apparatus for producing, by extrusion, flat profiled articles of plastic mixtures of various compositions of rubber or synthetic material, especially for producing uncured tread strips for pneumatic tires having a dual-layer central portion, and two identical edge portions; the apparatus has two first extruders, which are disposed at an acute angle above or next to one another and convey material to a common extrusion nozzle, and one third extruder, which is placed on the common extrusion nozzle and conveys material thereto counter to the direction in which the profiled articles are withdrawn from the apparatus.
2. Description of the Prior Art
It is known to produce multi-layer profiled articles by combining the partial flows of differing mixtures coming from several individual extruders in a common nozzle simultaneously with the shaping or immediately prior thereto, and to extrude the unit as a continuous, uniform article ln practice, advantageous use of this method has been made for a long time, for example to produce the uncured tread strips for pneumatic vehicle tires. Since the tread strips should have different properties in the different cross-sectional regions, not only for acceptable incorporation into the tire blank, but also for the use of the finished tire in driving operation, the tread strips generally have to be composed of two or more different elastomeric mixtures. However, the thorough combination of the partial streams in a single extruder head which is common to all of the extruders poses considerable rheological problems which become even worse if the individual flow paths of greatly different lengths, as is the case, for example, for tread strips having a specific mixture formulation for the widely spreadapart narrow edge portions. With known measures, such as coordinating the dimensions of the flow cross-sections with one another, employing flow suppressors, etc., these difficulties cannot be satisfactorily overcome, as a result of which delamination and other irregularities of the finished profiled articles constantly occur. The conditions improve when the third extruder in the known Y-arrangement is placed on the extrusion nozzle counter to the direction of withdrawal. However, the tight fastening of the three extruders together, or even the easily detachable clamping together, for example with the aid of bayonet closures, makes it necessary to have extremely heavy and expensive special constructions for such extruder heads.
In contrast, it is an object of the present invention, for the Y-arrangement of three extruders relative to one another, to provide, with structurally simple means which are consequently inexpensive to produce, a reliably tight and yet easily detachable connection, especially of the third extruder.